We investigate theoretically the self-focusing dynamics of an ultrashort la
ser pulse both near and above the threshold at which the pulse effectively
undergoes catastrophic collapse. We find that, as a result of space-time fo
cusing and self-steepening, an "optical shock" wave forms inside the medium
that gives rise to a broad blueshifted pedestal in the transmitted pulse s
pectrum. Out results are in good agreement with the primary features observ
ed in experiments and thus provide a theoretical understanding for the unde
rlying process that gives rise to "white-light" generation.